Photoelectric conversion elements are used in various photosensors, copying machines, solar cells, and the like. These photoelectric conversion elements have adopted various systems to be put into use, such as elements utilizing metals, elements utilizing semiconductors, elements utilizing organic pigments or dyes, or combinations of these elements. In particular, solar cells that make use of non-exhaustive solar energy do not necessitate fuels, and full-fledged practicalization of solar cells as an inexhaustible clean energy is being highly expected. Among these, research and development of silicon-based solar cells have long been in progress. Many countries also support policy-wise considerations, and thus dissemination of silicon-based solar cells is still in progress. However, silicon is an inorganic material, and has its own limitations in terms of improving throughput and cost, and the like.
Under such circumstances, research is being vigorously carried out on dye-sensitized solar cells. Especially, to have built momentum toward such research is research results by Graetzel et al. of École Polytechnique Fédérale de Lausanne in Switzerland (see Patent Literature 1). They employed a structure in which a dye formed from a ruthenium complex was fixed at the surface of a porous titanium oxide thin film, and realized a conversion efficiency that was comparable to that of amorphous silicon. Thus, the dye-sensitized solar cells that can be produced even without using an expensive vacuum apparatus instantly attracted the attention of researchers all over the world.
Hitherto, as metal complex dyes to be used in photoelectric conversion elements, dyes generally called as N3, N719, Z907, and J2 have been developed.
Meanwhile, recently, a ruthenium metal complex dye having a bidentate or tridentate ligand having a specific aromatic-ring anion at the coordination atom of a ligand, is being suggested (see Patent Literature 2 or 3). In addition, a ruthenium metal complex dye having a specific ligand combination using (pyridylazo)resorcinol, and the like, as a bidentate ligand, is also known (see Patent Literature 1). However, the improvements of durability and photoelectric conversion efficiency in a long wavelength range of 900 nm or more are not always satisfactory.